Don't forget that the DC descriptions are relative and cover all characters, trained and untrained, from level 1 to 20. A DC20 strength check may be nearly impossible for you, but it is easy for the level 20 soldier trained in athletics and a 20 in strength. That character gets a +11 to their roll.I'm not a trained athlete and I reckon my strength is just above average - maybe 11. If someone described a physical task as 'easy' I would expect that I had a greater than 50% chance of success. But in 5th edition the DC for an easy task is 10, which means, with no bonuses for proficiency or strength, it's a coin-flip.
'Difficult' (at DC20) is almost impossible.
I am less concerned about this from the perspective of character failure and more from the DM's point of view: straightforward language such as 'very easy, easy, moderate, difficult' is very useful when improvising DCs on the fly. I don't want to have to redefine what 'easy' means every time I use the word in that context (for example, by reminding myself that it means 'easy' only if you're trained, high-level and above average in ability).
Ability checks and skill checks are a big part of the game and I don't think they've got the DCs right at all.
In a calm situation, your character with a strength of 11 can take 10 on his strength roll. This represents taking your time and being careful about it. You would then hit the Easy DC of 10 ever time. Under a combat or rushed situation, your wizard would still make it 55% of the time. Easy still seems like an appropriate descriptor for DC10 to me since an untrained character with a 10 stat can succeed 100% of the time when they can take their time.
I have a list of my players relevant information (AC, stats, ideals, etc.) so I know what their passive check would be. I will just move things along if I know that it is a calm situation and everyone can succeed by taking 10. Otherwise, you repeatedly run into the situation where someone flubs a die roll and it slows the action down.